1. Field of the Invention
The present invention relates to the technical field of magnetic resonance imaging, and in particular, to a method for magnetic resonance imaging.
2. Description of the Prior Art
During a heating operation to a target area monitored by magnetic resonance imaging (MRI), a magnetic resonance imaging device can monitor the temperature changes of the target area so as to monitor the process and effects of the heating in real time. A common method for temperature measurement in magnetic resonance imaging is to perform a temperature imaging utilizing the fact that the proton resonance frequency (PRF) in water skews as the temperature changes so as to obtain a temperature image. Generally, a gradient echo sequence is utilized to perform a PRF skew-based magnetic resonance temperature imaging. In order to monitor the temperature of the target area in real time, it is required that the time resolution of the temperature imaging sequence be very high. In order to achieve this object, in the prior art the parameters of the temperature imaging sequence are optimized and short repeat time (TR), low spatial resolution, etc. are utilized. However, at the same time, from the viewpoint of the applications, it is also necessary to have an anatomical image with relatively high spatial resolution for monitoring the position of the heated target area and the anatomical image of the target area must be capable of being updated in a timely manner during the heating process.
Generally, when using magnetic resonance temperature imaging to monitor heating, the data generated by the temperature imaging sequence is used to reconstruct an anatomical image, thus monitoring the target area. Since the parameter settings of the temperature imaging sequence have had the imaging time optimized, for example, by applying relatively few steps of phase encoding, the object of quick temperature monitoring is achieved. Since there are only a few steps of phase encoding, an anatomical image rebuilt on the basis of the data generated by the temperature imaging sequence has relatively low resolution and the contrast between tissues is relatively poor, therefore the requirements relating to the differentiation and location of the tissues and organs in the target area during the heating process cannot be fully satisfied. It can be seen that the currently available temperature imaging sequence for magnetic resonance imaging cannot satisfy at the same time the requirements relating to a high spatial resolution and a high time resolution.
In Chinese patent application 200710064914.4, by the inventors Li Guo-bin, Chung Yiu-Cho, Zhang Qiang, and Zhou Xiao-dong (corresponding to U.S. Pat. No. 7,521,930), in order to balance the time resolution and the spatial resolution of a temperature image, there is provided a method for accelerating the magnetic resonance temperature imaging. In that patent application, the method first determines a temperature change at an ultrasonic focus, then determines the ideal acceleration rate needed by the data collection, adjusts the variable density data sampling of K space, and reconstructs the data obtained by the sampling to form a temperature image.